1. Field of the Invention
Example embodiments of the present invention relate to a memory module, and more particularly, to a printed circuit board (PCB) for a memory module, a method of manufacturing the same, and a memory module/socket assembly.
2. Description of the Related Art
Generally, a memory module may include a printed circuit board (PCB) and contact pins or contact taps formed on the PCB. A memory module may be electrically connected to, for example, a socket provided on a main board of an electronic device.
FIG. 1 is a sectional view schematically illustrating a memory module/socket assembly according to the prior art.
Referring to FIG. 1, a memory module 10 may include a PCB 11 and a memory package 13 mounted on the PCB 11. The memory package 13 may be mounted on the PCB by, for example, solder balls 15. Contact taps 17 may be formed on both opposite surfaces of an end portion of the PCB 11.
The memory module 10 may be inserted into a groove 33 formed on a body of a module socket 30 assembled on a main board 20. The contact taps 17 may electrically contact contact pins 35 provided on an inner wall of the groove 33.
However, as a capacity of a semiconductor device, for example, a memory device, is increased, the number of modules for electrically connecting the memory device to an external device, for example, a personal computer (PC), and the number of contact pins 35 and contact taps 17 used for the electrical connection of the memory module 10 to the module socket 30 have increased.
For example, two hundred and forty (240) contact taps may be provided on surfaces of a PCB for a double data rate 2 (DDR2) memory module. However, in order to manufacture a higher density module, additional I/O pins for a power supply and ground may be necessary. Accordingly, the total of 240 contact taps (or contact pins) may be insufficient.
Furthermore, as the number of the contact pins or the contact taps has increased, insert force to appropriately insert a memory module in a module socket has increased from 6 Kgf to 8 Kgf. Thus, pressing force applied from the pins to the taps has also increased. The increase in the forces may cause defects in the memory modules.
FIGS. 2 through 4 are sectional views illustrating cracks generated on memory packages on a variety of type of memory module/socket assemblies according to the prior art.
Referring to FIG. 2, a memory package 23 may be disposed on a module board 21 with solder balls 25 interposed therebetween. Because an insert force of a memory module may increase as described with reference to FIG. 1, the memory package 23 may be cracked.
Referring to FIG. 3, two memory chips 33 may be stacked on a module board 31 with solder balls 35 interposed therebetween. When two or more memory chips 33 are stacked, the memory chips 33 may be supported on supporting panels 36. In this case, the solder balls 35 may be interposed between the supporting panels 36. Likewise, due to the increased insert force of a memory module, the memory chips 33 may be cracked as shown in FIG. 3.
Referring to FIG. 4, four memory chips 43 may be stacked on a module board 41. The memory chips 43 may be supported on supporting panels 46 and solder balls 45 may be interposed between the supporting panels 46. Likewise, due to an increased insert force of a memory module, the memory chips 43 may be cracked as shown in FIG. 4.
As described above, an increase of an insert force of a memory module may cause cracks on a memory package or memory chips, and especially, when a plurality of the memory chips are stacked, and because chips may be processed to be very thin, the chips may be more vulnerable to cracks.
FIGS. 5 and 6 are schematic views illustrating defects on contact tabs of the memory module/socket assembly depicted in FIG. 1.
A defective tab will be described with reference to FIGS. 1, 5 and 6.
Referring to FIGS. 1 and 5, contact taps 17 may be scratched by contact pins 35 due to insert force, thereby generating a scratched portion 18. The scratched portion 18 may cause a short circuit between adjacent contact taps 17. In addition, referring to FIG. 6, a variety of contaminated layers 19 may be formed on the contact taps 17. The contamination of the contact tap 17 may be caused by a memory package 13 mounted in the vicinity of the contact taps 17 and a device, for example, a capacitor mounted on a PCB 11. That is, solder or flux that may be used to mount the memory package 13 or a device 12 may be splashed onto the contact taps 17 creating the contaminated layers 19.
As described above, in a memory module structure, because contact taps may be formed on a surface of a PCB, which may be on the same surface whereon a memory package may be mounted, it may be difficult to increase the number of contact taps and further prevent contamination and scratches on the contact taps. Furthermore, since the PCB may be inserted into a socket, the memory package may easily crack by an insert force.